1. Field of the Invention
The present invention relates to an active matrix liquid crystal panel and a method for repairing defects therein, and more particularly to a LCD panel having a repairable configuration.
2. Description of the Related Art
In recent years, flat display panels using liquid crystal and the like as a display medium have become popular as display devices for computers, word processors, and TV sets. In particular, an active matrix liquid crystal panel having switching elements such as thin film transistors for respective pixels to drive the pixels individually is used for a display device which requires a high resolution such as VGA, S-VGA, and XGA and a huge number of pixels for display.
Such an active matrix liquid crystal panel has a pair of substrates sandwiching a liquid crystal layer there between. One of the pair of substrates is provided with switching elements (hereinafter referred to as an active matrix substrate) and includes an insulating substrate, scanning lines and signal lines formed on the insulating substrate to cross each other, switching elements formed in the vicinity of the respective crossings of the scanning lines and the signal lines, and pixel electrodes formed in a matrix and connected to the respective switching elements. The other substrate (hereinafter referred to as a opposing substrate) includes a common electrode.
FIG. 1 is a schematic diagram showing a configuration of one pixel on an active matrix substrate in accordance with a prior art. A liquid crystal panel having a plurality of pixels 10, each with a herringbone shape, is either called a SIPS (Super In-Plane Switching) mode liquid crystal panel or ASIPS (Advanced Super In-Plane Switching) mode liquid crystal panel.
A pair of scanning lines 13 and a pair of herringbone-shaped signal lines 12 enclose the region of the pixel 10. A first common electrode 11d is formed in the layer that the scanning lines 13 exist, and is parallel to the adjoining scanning line 13. Each pair of fork-shaped branches 11d′ extending from the first common electrode lid goes toward one of the scanning lines 13, and is accompanied by the adjoining signal line 12 in such manner that the signal line 12 is across the hollow area of the pair of the fork-shaped branches 11d′ without overlapping each other.
On the uppermost surface, a hollow second common electrode 11u almost overlaps the fork-shaped branches 11d′, the scanning lines 13, and the signal lines 12, and a zigzag comb-shaped pixel electrode 14 is enclosed by the second common electrode 11u. A switching device 15 formed at the intersection of the signal line 12 and the scanning line 13 is connected to the signal line 12, the scanning line 13 and the pixel electrode 14 by its three terminals. Two branches 11u′ extending from the second common electrode 11u go toward the first common electrode 11d. Three branches 141 extending from the pixel electrode 14 like the teeth of a comb go toward the direction in opposition to the branches 11u′. Two branches 11u′ and three branches 141 are alternately arranged for a herringbone-shaped structure where horizontal electrical fields exist.
FIG. 2 shows the cross-section along line 1—1 of FIG. 1. All layers are stacked on a transparent substrate 16, such as a glass substrate. When the first common electrode 11d and the scanning lines 13 are formed on the transparent substrate 16, an insulator layer 17 is overlaid thereon. Then, the signal lines 12 formed on the insulator layer 17 is sequentially stacked with a passive layer 18, such as a SiNx film, and an organic insulator layer 19. On the uppermost surface of the active matrix substrate, there are the second common electrode 11u, the branches 11u′ and the branches 141, and all of them are made of ITO (indium-tin-oxide).
The drawback of the structure disclosed in the pixel 10 is the lack of a repairable layout for repairing damaged pixels caused by a broken signal line. Therefore, a liquid crystal panel with a large size or high resolution is more difficult to repair defects related to broken signal lines.